Chroma quantization parameter (qp) offset

ABSTRACT

Provided are systems, methods, and computer-readable medium for encoding and decoding video data. In various examples, a coding device can include multiple luma QP and chroma QP relationship tables. In performing quantization or inverse quantization one video data being encoded or decoded, respectively, the coding device can select a table. The table can be selected based on, for example, a slice type, a prediction mode, and/or a luminance value, among other factors. The coding device can then use the luma QP value to look up a chroma QP value from the table. The luma QP and chroma QP values can then be used in quantization or inverse quantization.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claim priority to U.S. Provisional Application No.62/574,686, filed on Oct. 19, 2017, which is hereby incorporated byreference herein in its entirety.

FIELD

This application is generally related to video coding. For example,systems and methods are related to defining chroma quantizationparameter (QP) difference (or “offset”) in relation to luma QP.

BRIEF SUMMARY

Provided are systems, methods, and computer-readable medium for encodingand decoding video data. In various examples, coding efficiency and/orquality of encoded video can be improved upon by using multiple luma QPand chroma QP relationship tables, and adaptively selecting among thetables according to a current coding situation.

In various examples, methods, coding devices (including encoding devicesand decoding devices), computer-readable medium, and apparatuses aredescribed that implement various techniques for encoding video data.These techniques can include obtaining, at an encoding device, videodata. The encoding device can include, for example, a memory for storingthe video data and a processor configured to perform the describedtechniques. The techniques can further include selecting, for a portionof the video data, a particular lookup table from a plurality of lookuptables, wherein each of the plurality of lookup tables definesrelationships between luma quantization parameter values and chromaquantization parameter values. The techniques can further includedetermining, for a coding unit from the portion of the video data, aluma quantization parameter value. The techniques can further includedetermining, for the coding unit, a chroma quantization parameter value,wherein the chroma quantization parameter value is determined by usingthe luma quantization parameter value to look up the chroma quantizationparameter value in the particular lookup table. The techniques canfurther include performing quantization on the coding unit using theluma quantization parameter value and the chroma quantization parametervalue. The techniques can further include generating encoded video datausing values determined from performing quantization on the coding unit.

In some aspects, the described techniques can further includedetermining a slice type for the portion of the video data. In theseaspects, the particular lookup table is selected using the slice type.

In some aspects, the described techniques can further includedetermining a prediction mode for the portion of the video data. Inthese aspects, the particular lookup table is selected using theprediction mode.

In some aspects, the described techniques can further includedetermining a luminance value for a pixel in the portion of the videodata. In these aspects, the particular lookup table is selected usingthe luminance value.

In some aspects, the encoded video data includes an index thatidentifies the particular lookup table.

In some aspects, the described techniques can further include encodingthe particular table into the encoded video data.

In some aspects, encoding device the implements the described techniquescan include a camera for capturing video data.

In various examples, methods, coding devices (including encoding devicesand decoding devices), computer-readable medium, and apparatuses aredescribed that implement various techniques for decoding video data. Thetechniques can include obtaining, at a coding device, encoded videodata. The coding device can include, for example, a memory for storingthe encoding video data and a processor configured to perform thedescribed techniques. The techniques can further include selecting, fora portion of the encoded video data, a particular lookup table from aplurality of lookup tables, wherein each of the plurality of lookuptables defines a relationship between luma quantization parameter valuesand chroma quantization parameter values. The techniques can furtherinclude determining, for a coding unit from the portion of the encodedvideo data, a luma quantization parameter value. The techniques canfurther include determining, for the coding unit, a chroma quantizationparameter value, wherein the chroma quantization parameter value isdetermined by using the luma quantization parameter value to look up thechroma quantization parameter value in the particular lookup table. Thetechniques can further include performing inverse quantization on thecoding unit using the luma quantization parameter value and the chromaquantization parameter value. The techniques can further include.decoding the portion of the encoded video data using results fromperforming inverse quantization on the coding unit.

In some aspects, the described techniques can further includedetermining a slice type for the portion of the encoded video data. Inthese aspects, the particular lookup table is selected using the slicetype.

In some aspects, the described techniques can further includedetermining a prediction mode for the portion of the encoded video data.In these aspects, the particular lookup table is selected using theprediction mode.

In some aspects, the described techniques can further includedetermining a luminance value for a pixel in the portion of the encodedvideo data. In these aspects, the particular lookup table is selectedusing the luminance value.

In some aspects, the described techniques can further includedetermining, from the encoded video data, an index. In these aspects,the particular lookup table is selected using the index.

In some aspects, the described techniques can further include decodingthe particular lookup table from the encoded video data.

In some aspects the coding device includes a camera for capturing videodata. In some aspects, the coding device includes a display fordisplaying decoded video data. In some aspects, the coding devicecomprises a mobile device.

In some aspects, an apparatus can include means for performing thedescribed techniques. In these aspects, the apparatus can include, forexample, integrated circuitry operable to execute program instructions,where the program instructions can perform steps of the describedtechniques. The apparatus can further include memories for storing thevideo data, intermediate values generated when encoding the video data,and/or encoded video data that results from performing the techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present application are described indetail below with reference to the following drawing figures:

FIG. 1 is a block diagram illustrating an example of an encoding deviceand a decoding device, in accordance with some examples.

FIG. 2 includes a diagram of a lower resolution video frame.

FIG. 3 includes a diagram of a higher resolution video frame.

FIG. 4 includes a block diagram of a quantization unit that can beincluded in an encoding device.

FIG. 5 includes a block diagram illustrating an example of an inversequantization unit that can be included in an encoding device or adecoding device.

FIG. 6 includes a flowchart illustrating an example of a process forencoding video data.

FIG. 7 includes a flowchart illustrating an example of a process fordecoding video data.

FIG. 8 is a block diagram illustrating an example video encoding device,in accordance with some examples.

FIG. 9 is a block diagram illustrating an example video decoding device,in accordance with some examples.

DETAILED DESCRIPTION

Certain aspects and examples disclosure are provided below. Some ofthese aspects and examples may be applied independently and some of themmay be applied in combination as would be apparent to those of skill inthe art. In the following description, for the purposes of explanation,specific details are set forth in order to provide a thoroughunderstanding of the various examples discussed herein. However, it willbe apparent that various examples may be practiced without thesespecific details. The figures and description are not intended to berestrictive.

The ensuing description provides example implementations only, and isnot intended to limit the scope, applicability, or configuration of thedisclosure. Rather, the ensuing description of the exampleimplementations will provide those skilled in the art with an enablingdescription for implementing an example implementation. It should beunderstood that various changes may be made in the function andarrangement of elements without departing from the spirit and scope ofthe application as set forth in the appended claims.

Specific details are given in the following description to provide athorough understanding of the examples. However, it will be understoodby one of ordinary skill in the art that the examples may be practicedwithout these specific details. For example, circuits, systems,networks, processes, and other components may be shown as components inblock diagram form in order not to obscure the embodiments inunnecessary detail. In other instances, well-known circuits, processes,algorithms, structures, and techniques may be shown without unnecessarydetail in order to avoid obscuring the examples.

Also, it is noted that individual examples may be described as a processwhich is depicted as a flowchart, a flow diagram, a data flow diagram, astructure diagram, or a block diagram. Although a flowchart may describethe operations as a sequential process, many of the operations can beperformed in parallel or concurrently. In addition, the order of theoperations may be re-arranged. A process is terminated when itsoperations are completed, but could have additional steps not includedin a figure. A process may correspond to a method, a function, aprocedure, a subroutine, a subprogram, etc. When a process correspondsto a function, its termination can correspond to a return of thefunction to the calling function or the main function.

The term “computer-readable medium” includes, but is not limited to,portable or non-portable storage devices, optical storage devices, andvarious other mediums capable of storing, containing, or carryinginstruction(s) and/or data. A computer-readable medium may include anon-transitory medium in which data can be stored and that does notinclude carrier waves and/or transitory electronic signals propagatingwirelessly or over wired connections. Examples of a non-transitorymedium may include, but are not limited to, a magnetic disk or tape,optical storage media such as compact disk (CD) or digital versatiledisk (DVD), flash memory, memory or memory devices. A computer-readablemedium may have stored thereon code and/or machine-executableinstructions that may represent a procedure, a function, a subprogram, aprogram, a routine, a subroutine, a module, a software package, a class,or any combination of instructions, data structures, or programstatements. A code segment may be coupled to another code segment or ahardware circuit by passing and/or receiving information, data,arguments, parameters, or memory contents. Information, arguments,parameters, data, etc. may be passed, forwarded, or transmitted via anysuitable means including memory sharing, message passing, token passing,network transmission, or the like.

Furthermore, examples may be implemented by hardware, software,firmware, middleware, microcode, hardware description languages, or anycombination thereof. When implemented in software, firmware, middlewareor microcode, the program code or code segments to perform the necessarytasks (e.g., a computer-program product) may be stored in acomputer-readable or machine-readable medium. A processor(s) may performthe necessary tasks.

As more devices and systems provide consumers with the ability toconsume digital video data, the need for efficient video codingtechniques becomes more important. Video coding is needed to reducestorage and transmission requirements necessary to handle the largeamounts of data present in digital video data. Various video codingtechniques may be used to compress video data into a form that uses alower bit rate while maintaining high video quality.

In various video coding processes, the chroma quantization parameter(QP) is derived from QP value for the luma component. Various videocoding processes use a lookup table to perform the derivation, where theluma QP value is used as an index to find a corresponding chroma QP.This lookup table can be referred to as a QP offset table, due to thechroma QP values being defined as an offsets from the luma QP values.

For some video coding processes, the lookup table was defined for lowerresolution video sequences and legacy video capture devices (e.g., thosecapturing 1080p or lower resolutions). In higher resolution videosequences, such as high-definition (HD) and ultra-high-definition (UHD)video, the differences in chroma values between neighboring pixels maybe smaller, such that the chroma component of a picture can be smootherthan the luma component. Using lookup tables defined for thelower-resolution video sequences, however, can result in loss of detailin the chroma component.

Systems and methods are described herein for defining a chromaquantization parameter (QP) difference (offset) in relation to Luma QP.Such systems and methods can be used in the context of advanced videocodecs, which can include, for example, HEVC codecs, codecs usingextensions of HEVC, codecs using the next generation of video codingstandards, and/or other suitable video codec. In various examples,instead of using a fixed QP offset table, a video coding system canadaptively select from among multiple QP offset tables. For example, thevideo coding system can use a slice type, a prediction mode, or aluminance value to select a QP offset table. By using these and otherselection criteria, chroma QP values that better reflect the content ofa video frame can be used.

FIG. 1 is a block diagram illustrating an example of a system 100including an encoding device 104 and a decoding device 112. The encodingdevice 104 may be part of a source device, and the decoding device 112may be part of a receiving device. The source device and/or thereceiving device may include an electronic device, such as a mobile orstationary telephone handset (e.g., smartphone, cellular telephone, orthe like), a desktop computer, a laptop or notebook computer, a tabletcomputer, a set-top box, a television, a camera, a display device, adigital media player, a video gaming console, a video streaming device,an Internet Protocol (IP) camera, or any other suitable electronicdevice. In some examples, the source device and the receiving device mayinclude one or more wireless transceivers for wireless communications.The coding techniques described herein are applicable to video coding invarious multimedia applications, including streaming video transmissions(e.g., over the Internet), television broadcasts or transmissions,encoding of digital video for storage on a data storage medium, decodingof digital video stored on a data storage medium, or other applications.In some examples, system 100 can support one-way or two-way videotransmission to support applications such as video conferencing, videostreaming, video playback, video broadcasting, gaming, and/or videotelephony.

The encoding device 104 (or encoder) can be used to encode video datausing a video coding standard or protocol to generate an encoded videobitstream. Video coding standards include ITU-T H.261, ISO/IEC MPEG-1Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IECMPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC),including its Scalable Video Coding (SVC) and Multi-view Video Coding(MVC) extensions. In addition, a new video coding standard, namely HighEfficiency Video Coding (HEVC), has been developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).The latest HEVC draft specification, and referred to as HEVC WDhereinafter, is available from http://phenix.int-evry.fr/jct/doc enduser/documents/14 Vienna/wg11/JCTVC-N1003-vl.zip. ITU-T VCEG (Q6/16) andISO/IEC MPEG (JTC 1/SC 29/WG 11) are now studying the potential need forstandardization of future video coding technology with a compressioncapability that significantly exceeds that of the current HEVC standard(including its current extensions and near-term extensions for screencontent coding and high-dynamic-range coding). The groups are workingtogether on this exploration activity in a joint collaboration effortknown as the Joint Video Exploration Team (JVET) to evaluate compressiontechnology designs proposed by their experts in this area. The JVETfirst met during 19-21 Oct. 2015. And the latest version of referencesoftware, i.e., Joint Exploration Model 5.0.1 (JEM 5.0.1) is availableathttps://jvet.hhi.fraunhofer.de/svn/svn_HMJEMSoftware/tags/HM-16.6-JEM-5.0.1/.

Many examples described herein provide examples using the JEM model, theHEVC standard, and/or extensions thereof. However, the techniques andsystems described herein may also be applicable to other codingstandards, such as AVC, MPEG, extensions thereof, or other suitablecoding standards already available or not yet available or developed.Accordingly, while the techniques and systems described herein may bedescribed with reference to a particular video coding standard, one ofordinary skill in the art will appreciate that the description shouldnot be interpreted to apply only to that particular standard. Herein,video coding can refer to encoding and/or decoding.

Referring to FIG. 1, a video source 102 may provide the video data tothe encoding device 104. The video source 102 may be part of the sourcedevice, or may be part of a device other than the source device. Thevideo source 102 may include a video capture device (e.g., a videocamera, a camera phone, a video phone, or the like), a video archivecontaining stored video, a video server or content provider providingvideo data, a video feed interface receiving video from a video serveror content provider, a computer graphics system for generating computergraphics video data, a combination of such sources, or any othersuitable video source.

The video data from the video source 102 may include one or more inputpictures or frames. A picture or frame is a still image that is part ofa video. The encoder engine 106 (or encoder) of the encoding device 104encodes the video data to generate an encoded video bitstream. In someexamples, an encoded video bitstream (or “video bitstream” or“bitstream”) is a series of one or more coded video sequences. A codedvideo sequence (CVS) includes a series of access units (AUs) startingwith an AU that has a random access point picture in the base layer andwith certain properties up to and not including a next AU that has arandom access point picture in the base layer and with certainproperties. For example, the certain properties of a random access pointpicture that starts a CVS may include a RASL flag (e.g.,NoRaslOutputFlag) equal to 1. Otherwise, a random access point picture(with RASL flag equal to 0) does not start a CVS. An access unit (AU)includes one or more coded pictures and control informationcorresponding to the coded pictures that share the same output time.Coded slices of pictures are encapsulated in the bitstream level intodata units called network abstraction layer (NAL) units. For example, anHEVC video bitstream may include one or more CVSs including NAL units.Each of the NAL units has a NAL unit header. In one example, the headeris one-byte for H.264/AVC (except for multi-layer extensions) andtwo-byte for HEVC. The syntax elements in the NAL unit header take thedesignated bits and therefore are visible to all kinds of systems andtransport layers, such as Transport Stream, Real-time Transport (RTP)Protocol, File Format, among others.

Two classes of NAL units exist in the HEVC standard, including videocoding layer (VCL) NAL units and non-VCL NAL units. A VCL NAL unitincludes one slice or slice segment (described below) of coded picturedata, and a non-VCL NAL unit includes control information that relatesto one or more coded pictures. In some cases, a NAL unit can be referredto as a packet. An HEVC AU includes VCL NAL units containing codedpicture data and non-VCL NAL units (if any) corresponding to the codedpicture data.

NAL units may contain a sequence of bits forming a coded representationof the video data (e.g., an encoded video bitstream, a CVS of abitstream, or the like), such as coded representations of pictures in avideo. The encoder engine 106 generates coded representations ofpictures by partitioning each picture into multiple slices. A slice isindependent of other slices so that information in the slice is codedwithout dependency on data from other slices within the same picture. Aslice includes one or more slice segments including an independent slicesegment and, if present, one or more dependent slice segments thatdepend on previous slice segments. The slices are then partitioned intocoding tree blocks (CTBs) of luma samples and chroma samples. A CTB ofluma samples and one or more CTBs of chroma samples, along with syntaxfor the samples, are referred to as a coding tree unit (CTU). A CTU isthe basic processing unit for HEVC encoding. A CTU can be split intomultiple coding units (CUs) of varying sizes. A CU contains luma andchroma sample arrays that are referred to as coding blocks (CBs).

The luma and chroma CBs can be further split into prediction blocks(PBs). A PB is a block of samples of the luma component or a chromacomponent that uses the same motion parameters for inter-prediction orintra-block copy prediction (when available or enabled for use). Theluma PB and one or more chroma PBs, together with associated syntax,form a prediction unit (PU). For inter-prediction, a set of motionparameters (e.g., one or more motion vectors, reference indices, or thelike) is signaled in the bitstream for each PU and is used forinter-prediction of the luma PB and the one or more chroma PBs. Themotion parameters can also be referred to as motion information. A CBcan also be partitioned into one or more transform blocks (TBs). A TBrepresents a square block of samples of a color component on which thesame two-dimensional transform is applied for coding a predictionresidual signal. A transform unit (TU) represents the TBs of luma andchroma samples, and corresponding syntax elements.

A size of a CU corresponds to a size of the coding mode and may besquare in shape. For example, a size of a CU may be 8×8 samples, 16×16samples, 32×32 samples, 64×64 samples, or any other appropriate size upto the size of the corresponding CTU. The phrase “N×N” is used herein torefer to pixel dimensions of a video block in terms of vertical andhorizontal dimensions (e.g., 8 pixels×8 pixels). The pixels in a blockmay be arranged in rows and columns. In some examples, blocks may nothave the same number of pixels in a horizontal direction as in avertical direction. Syntax data associated with a CU may describe, forexample, partitioning of the CU into one or more PUs. Partitioning modesmay differ between whether the CU is intra-prediction mode encoded orinter-prediction mode encoded. PUs may be partitioned to be non-squarein shape. Syntax data associated with a CU may also describe, forexample, partitioning of the CU into one or more TUs according to a CTU.A TU can be square or non-square in shape.

According to the HEVC standard, transformations may be performed usingtransform units (TUs). TUs may vary for different CUs. The TUs may besized based on the size of PUs within a given CU. The TUs may be thesame size or smaller than the PUs. In some examples, residual samplescorresponding to a CU may be subdivided into smaller units using aquadtree structure known as residual quad tree (RQT). Leaf nodes of theRQT may correspond to TUs. Pixel difference values associated with theTUs may be transformed to produce transform coefficients. The transformcoefficients may then be quantized by the encoder engine 106.

Once the pictures of the video data are partitioned into CUs, theencoder engine 106 predicts each PU using a prediction mode. Theprediction unit or prediction block is then subtracted from the originalvideo data to get residuals (described below). For each CU, a predictionmode may be signaled inside the bitstream using syntax data. Aprediction mode may include intra-prediction (or intra-pictureprediction) or inter-prediction (or inter-picture prediction).Intra-prediction utilizes the correlation between spatially neighboringsamples within a picture. For example, using intra-prediction, each PUis predicted from neighboring image data in the same picture using, forexample, DC prediction to find an average value for the PU, planarprediction to fit a planar surface to the PU, direction prediction toextrapolate from neighboring data, or any other suitable types ofprediction. Inter-prediction uses the temporal correlation betweenpictures in order to derive a motion-compensated prediction for a blockof image samples. For example, using inter-prediction, each PU ispredicted using motion compensation prediction from image data in one ormore reference pictures (before or after the current picture in outputorder). The decision whether to code a picture area using inter-pictureor intra-picture prediction may be made, for example, at the CU level.

In some examples, the one or more slices of a picture are assigned aslice type. Slice types include an I slice, a P slice, and a B slice. AnI slice (intra-frames, independently decodable) is a slice of a picturethat is only coded by intra-prediction, and therefore is independentlydecodable since the I slice requires only the data within the frame topredict any prediction unit or prediction block of the slice. A P slice(uni-directional predicted frames) is a slice of a picture that may becoded with intra-prediction and with uni-directional inter-prediction.Each prediction unit or prediction block within a P slice is eithercoded with Intra prediction or inter-prediction. When theinter-prediction applies, the prediction unit or prediction block isonly predicted by one reference picture, and therefore reference samplesare only from one reference region of one frame. A B slice(bi-directional predictive frames) is a slice of a picture that may becoded with intra-prediction and with inter-prediction (e.g., eitherbi-prediction or uni-prediction). A prediction unit or prediction blockof a B slice may be bi-directionally predicted from two referencepictures, where each picture contributes one reference region and samplesets of the two reference regions are weighted (e.g., with equal weightsor with different weights) to produce the prediction signal of thebi-directional predicted block. As explained above, slices of onepicture are independently coded. In some cases, a picture can be codedas just one slice.

A PU may include the data (e.g., motion parameters or other suitabledata) related to the prediction process. For example, when the PU isencoded using intra-prediction, the PU may include data describing anintra-prediction mode for the PU. As another example, when the PU isencoded using inter-prediction, the PU may include data defining amotion vector for the PU. The data defining the motion vector for a PUmay describe, for example, a horizontal component of the motion vector(Δx), a vertical component of the motion vector (Δy), a resolution forthe motion vector (e.g., integer precision, one-quarter pixel precisionor one-eighth pixel precision), a reference picture to which the motionvector points, a reference index, a reference picture list (e.g., List0, List 1, or List C) for the motion vector, or any combination thereof.

The encoding device 104 may then perform transformation andquantization. For example, following prediction, the encoder engine 106may calculate residual values corresponding to the PU. Residual valuesmay comprise pixel difference values between the current block of pixelsbeing coded (the PU) and the prediction block used to predict thecurrent block (e.g., the predicted version of the current block). Forexample, after generating a prediction block (e.g., issuinginter-prediction or intra-prediction), the encoder engine 106 cangenerate a residual block by subtracting the prediction block producedby a prediction unit from the current block. The residual block includesa set of pixel difference values that quantify differences between pixelvalues of the current block and pixel values of the prediction block. Insome examples, the residual block may be represented in atwo-dimensional block format (e.g., a two-dimensional matrix or array ofpixel values). In such examples, the residual block is a two-dimensionalrepresentation of the pixel values.

Any residual data that may be remaining after prediction is performed istransformed using a block transform, which may be based on discretecosine transform, discrete sine transform, an integer transform, awavelet transform, other suitable transform function, or any combinationthereof. In some cases, one or more block transforms (e.g., sizes 32×32,16×16, 8×8, 4×4, or other suitable size) may be applied to residual datain each CU. In some examples, a TU may be used for the transform andquantization processes implemented by the encoder engine 106. A given CUhaving one or more PUs may also include one or more TUs. As described infurther detail below, the residual values may be transformed intotransform coefficients using the block transforms, and then may bequantized and scanned using TUs to produce serialized transformcoefficients for entropy coding.

In some examples, following intra-predictive or inter-predictive codingusing PUs of a CU, the encoder engine 106 may calculate residual datafor the TUs of the CU. The PUs may comprise pixel data in the spatialdomain (or pixel domain). The TUs may comprise coefficients in thetransform domain following application of a block transform. Aspreviously noted, the residual data may correspond to pixel differencevalues between pixels of the unencoded picture and prediction valuescorresponding to the PUs. Encoder engine 106 may form the TUs includingthe residual data for the CU, and may then transform the TUs to producetransform coefficients for the CU.

The encoder engine 106 may perform quantization of the transformcoefficients. Quantization provides further compression by quantizingthe transform coefficients to reduce the amount of data used torepresent the coefficients. For example, quantization may reduce the bitdepth associated with some or all of the coefficients. In one example, acoefficient with an n-bit value may be rounded down to an m-bit valueduring quantization, with n being greater than m.

Once quantization is performed, the coded video bitstream includesquantized transform coefficients, prediction information (e.g.,prediction modes, motion vectors, block vectors, or the like),partitioning information, and any other suitable data, such as othersyntax data. The different elements of the coded video bitstream maythen be entropy encoded by the encoder engine 106. In some examples, theencoder engine 106 may utilize a predefined scan order to scan thequantized transform coefficients to produce a serialized vector that canbe entropy encoded. In some examples, encoder engine 106 may perform anadaptive scan. After scanning the quantized transform coefficients toform a vector (e.g., a one-dimensional vector), the encoder engine 106may entropy encode the vector. For example, the encoder engine 106 mayuse context adaptive variable length coding, context adaptive binaryarithmetic coding, syntax-based context-adaptive binary arithmeticcoding, probability interval partitioning entropy coding, or anothersuitable entropy encoding technique.

As previously described, an HEVC bitstream includes a group of NALunits, including VCL NAL units and non-VCL NAL units. VCL NAL unitsinclude coded picture data forming a coded video bitstream. For example,a sequence of bits forming the coded video bitstream is present in VCLNAL units. Non-VCL NAL units may contain parameter sets with high-levelinformation relating to the encoded video bitstream, in addition toother information. For example, a parameter set may include a videoparameter set (VPS), a sequence parameter set (SPS), and a pictureparameter set (PPS). Examples of goals of the parameter sets include bitrate efficiency, error resiliency, and providing systems layerinterfaces. Each slice references a single active PPS, SPS, and VPS toaccess information that the decoding device 112 may use for decoding theslice. An identifier (ID) may be coded for each parameter set, includinga VPS ID, an SPS ID, and a PPS ID. An SPS includes an SPS ID and a VPSID. A PPS includes a PPS ID and an SPS ID. Each slice header includes aPPS ID. Using the IDs, active parameter sets can be identified for agiven slice.

A PPS includes information that applies to all slices in a givenpicture. Because of this, all slices in a picture refer to the same PPS.Slices in different pictures may also refer to the same PPS. An SPSincludes information that applies to all pictures in a same coded videosequence (CVS) or bitstream. As previously described, a coded videosequence is a series of access units (AUs) that starts with a randomaccess point picture (e.g., an instantaneous decode reference (IDR)picture or broken link access (BLA) picture, or other appropriate randomaccess point picture) in the base layer and with certain properties(described above) up to and not including a next AU that has a randomaccess point picture in the base layer and with certain properties (orthe end of the bitstream). The information in an SPS may not change frompicture to picture within a coded video sequence. Pictures in a codedvideo sequence may use the same SPS. The VPS includes information thatapplies to all layers within a coded video sequence or bitstream. TheVPS includes a syntax structure with syntax elements that apply toentire coded video sequences. In some embodiments, the VPS, SPS, or PPSmay be transmitted in-band with the encoded bitstream. In someembodiments, the VPS, SPS, or PPS may be transmitted out-of-band in aseparate transmission than the NAL units containing coded video data.

A video bitstream can also include Supplemental Enhancement Information(SEI) messages. For example, an SEI NAL unit can be part of the videobitstream. In some cases, an SEI message can contain information that isnot needed by the decoding process. For example, the information in anSEI message may not be essential for the decoder to decode the videopictures of the bitstream, but the decoder can be use the information toimprove the display or processing of the pictures (e.g., the decodedoutput). The information in an SEI message can be embedded metadata. Inone illustrative example, the information in an SEI message could beused by decoder-side entities to improve the viewability of the content.In some instances, certain application standards may mandate thepresence of such SEI messages in the bitstream so that the improvementin quality can be brought to all devices that conform to the applicationstandard (e.g., the carriage of the frame-packing SEI message forframe-compatible plano-stereoscopic 3DTV video format, where the SEImessage is carried for every frame of the video, handling of a recoverypoint SEI message, use of pan-scan scan rectangle SEI message in DVB, inaddition to many other examples).

The output 110 of the encoding device 104 may send the NAL units makingup the encoded video bitstream data over the communications link 120 tothe decoding device 112 of the receiving device. The input 114 of thedecoding device 112 may receive the NAL units. The communications link120 may include a channel provided by a wireless network, a wirednetwork, or a combination of a wired and wireless network. A wirelessnetwork may include any wireless interface or combination of wirelessinterfaces and may include any suitable wireless network (e.g., theInternet or other wide area network, a packet-based network, WiFi™,radio frequency (RF), UWB, WiFi-Direct, cellular, Long-Term Evolution(LTE), WiMax™, or the like). A wired network may include any wiredinterface (e.g., fiber, ethernet, powerline ethernet, ethernet overcoaxial cable, digital signal line (DSL), or the like). The wired and/orwireless networks may be implemented using various equipment, such asbase stations, routers, access points, bridges, gateways, switches, orthe like. The encoded video bitstream data may be modulated according toa communication standard, such as a wireless communication protocol, andtransmitted to the receiving device.

In some examples, the encoding device 104 may store encoded videobitstream data in storage 108. The output 110 may retrieve the encodedvideo bitstream data from the encoder engine 106 or from the storage108. Storage 108 may include any of a variety of distributed or locallyaccessed data storage media. For example, the storage 108 may include ahard drive, a storage disc, flash memory, volatile or non-volatilememory, or any other suitable digital storage media for storing encodedvideo data.

The input 114 of the decoding device 112 receives the encoded videobitstream data and may provide the video bitstream data to the decoderengine 116, or to storage 118 for later use by the decoder engine 116.The decoder engine 116 may decode the encoded video bitstream data byentropy decoding (e.g., using an entropy decoder) and extracting theelements of one or more coded video sequences making up the encodedvideo data. The decoder engine 116 may then rescale and perform aninverse transform on the encoded video bitstream data. Residual data isthen passed to a prediction stage of the decoder engine 116. The decoderengine 116 then predicts a block of pixels (e.g., a PU). In someexamples, the prediction is added to the output of the inverse transform(the residual data).

The decoding device 112 may output the decoded video to a videodestination device 122, which may include a display or other outputdevice for displaying the decoded video data to a consumer of thecontent. In some aspects, the video destination device 122 may be partof the receiving device that includes the decoding device 112. In someaspects, the video destination device 122 may be part of a separatedevice other than the receiving device.

Supplemental Enhancement Information (SEI) messages can be included invideo bitstreams. For example, SEI messages may be used to carryinformation (e.g., metadata) that is not essential in order to decodethe bitstream by the decoding device 112. This information is useful inimproving the display or processing of the decoded output (e.g. suchinformation could be used by decoder-side entities to improve theviewability of the content).

In some examples, the video encoding device 104 and/or the videodecoding device 112 may be integrated with an audio encoding device andaudio decoding device, respectively. The video encoding device 104and/or the video decoding device 112 may also include other hardware orsoftware that is necessary to implement the coding techniques describedabove, such as one or more microprocessors, digital signal processors(DSPs), application specific integrated circuits (ASICs), fieldprogrammable gate arrays (FPGAs), discrete logic, software, hardware,firmware or any combinations thereof. The video encoding device 104 andthe video decoding device 112 may be integrated as part of a combinedencoder/decoder (codec) in a respective device. An example of specificdetails of the encoding device 104 is described below with reference toFIG. 8. An example of specific details of the decoding device 112 isdescribed below with reference to FIG. 9.

As noted above, extensions to the HEVC standard include the Multi-viewVideo Coding extension (referred to as MVC or MV-HEVC), and the ScalableVideo Coding extension (referred to as SVC or SHVC). The MVC and SHVCextensions share the concept of layered coding, with different layersbeing included in the encoded video bitstream. Each layer in a codedvideo sequence is addressed by a unique layer identifier (ID). A layerID may be present in a header of a NAL unit to identify a layer withwhich the NAL unit is associated. In MV-HEVC, different layers usuallyrepresent different views of the same scene in the video bitstream. InSVC, different scalable layers are provided that represent the videobitstream in different spatial resolutions (or picture resolution) or indifferent reconstruction fidelities. The scalable layers may include abase layer (with layer ID=0) and one or more enhancement layers (withlayer IDs=1, 2, . . . n). The base layer may conform to a profile of thefirst version of HEVC, and represents the lowest available layer in abitstream. The enhancement layers have increased spatial resolution,temporal resolution or frame rate, and/or reconstruction fidelity (orquality) as compared to the base layer. The enhancement layers arehierarchically organized and may (or may not) depend on lower layers. Insome examples, the different layers may be coded using a single standardcodec (e.g., all layers are encoded using HEVC, SHVC, or other codingstandard). In some examples, different layers may be coded using amulti-standard codec. For example, a base layer may be coded using AVC,while one or more enhancement layers may be coded using SHVC and/orMV-HEVC extensions to the HEVC standard. In general, a layer includes aset of VCL NAL units and a corresponding set of non-VCL NAL units. TheNAL units are assigned a particular layer ID value. Layers can behierarchical in the sense that a layer may depend on a lower layer.

As noted above, during encoding of video data, an encoder can performquantization on transform coefficients, which are derived from residualvalues that result from motion estimation and/or motion prediction. Inanalog to digital conversion, quantization is a process by which analogvalues are rounded off to values that are approximately equal to theanalog values. The rounding process can result in a series of discrete,digital values that approximate an analog signal. The discreteamplitudes of the quantized output can be called representation levelsor reconstruction levels. The spacing between two adjacent levels can becalled the quantum or step-size. Smaller step sizes result in a closerapproximation of the analog signal and a larger number of quantizedoutput values, and thus a less compressed output. Larger step sizesresult in a less accurate representation of the analog size and fewerquantized output values, and thus a more compressed output.

In various video coding processes, the luma color component of a pixeland the chroma color components are quantized separately. Some videocoding processes include a procedure for deriving luma QP value, wherethe luma QP used for a coding block can depend on, for example, thecoding block's location in the video data, a previous luma QP valueused, and/or an encoding quality that was selected for the video data.

In various examples, the chroma QP value is derived from the luma QPusing a lookup table. Table 1 below illustrates an example of such alookup table. The lookup table of Table 1 provides chroma QP values forluma QP values defined for the HEVC standard. In various examples, thesame table is used for all slice types and all encoding modes. In someexamples, an additional chroma QP offset can be signaled (e.g., providedin) a slice header to change the luma QP-to-chroma QP relationship forall the blocks that are in the slice.

TABLE 1 Luma QP 0 1 2 3 4 5 6 7 8 Chroma QP 0 1 2 3 4 5 6 7 8 Luma QP 910 11 12 13 14 15 16 17 Chroma QP 9 10 11 12 13 14 15 16 17 Luma QP 1819 20 21 22 23 24 25 26 Chroma QP 18 19 20 21 22 23 24 25 26 Luma QP 2728 29 30 31 32 33 34 35 Chroma QP 27 28 29 29 30 31 32 33 33 Luma QP 3637 38 39 40 41 42 43 44 Chroma QP 34 34 35 35 36 36 37 37 38 Luma QP 4546 47 48 49 50 51 52 53 Chroma QP 39 40 41 42 43 44 45 46 47 Luma QP 5455 56 57 Chroma QP 48 49 50 51

In various coding standards, luma QP-to-chroma-QP offsets such as thoseprovided in Table 1 were defined for smaller resolution video sequencesand legacy video capture devices. At smaller resolutions, the differencein chroma values between neighboring pixels may be relatively large. Inhigh-definition (HD) and ultra-high-definition (UHD) video sequences,the differences in chroma values between neighboring pixels may besmaller, such that the chroma component of a picture can be smootherthan the luma component.

FIG. 2 includes a diagram of a lower resolution video frame 200. “Lowerresolution,” in this context, means less than HD quality, such as 720pixels wide and 576 pixels high, or less. The width and height of thevideo frame 200 is illustrated in the example of FIG. 2 by variables xand y, respectively. The grid drawn over the video frame 200 illustratesrepresentative pixel locations. A fewer number of pixel locations areillustrated than would be present in many lower resolution video frames,for the sake of clarity.

FIG. 2 further illustrates an example of the luma (Y) and chroma (Cr,Cb) values for set of four neighboring pixels 202. As illustrated bythis example, between this set of neighboring pixels 202, the chromavalues can have large transitions from one pixel to the neighboringpixel, due to the neighboring pixels capturing different information.The luma and chroma values in this example are merely illustrative ofpossible color values in a video frame. Luma and chroma values withsmaller and larger variations between neighboring pixels can also occur,depending on the content of the video frame.

FIG. 3 includes a diagram of a higher resolution video frame 300.“Higher resolution,” in this context, means at least HD quality, or atleast 1280 pixels wide by 720 pixels high. The width and height of thevideo frame 300 are illustrated by variables x and y, respectively. Thegrid drawn over the video frame 300 illustrates representative pixellocations, with fewer than an actual number of pixel locations beingillustrated, for the sake of clarity.

FIG. 3 further illustrates example luma and chroma values for a set ofnine neighboring pixels 302. In this example, the transitions betweenthe chroma values across the set of neighboring pixels changes moregradually than in the example of FIG. 2. This more gradual changereflects the higher degree of detail captured in the video frame 300 ofFIG. 3.

The fixed QP offset table illustrated in the example of Table 1 may beadequate for lower resolution video frames, where chroma values can varygreatly between neighboring pixels. In higher resolution video, however,the fixed QP offset table can result in undesirable loss of detail.Chroma QP values that accommodate smaller changes in the chroma valuescan preserve more detail. Additionally, improved video coding techniquescan improve the coding efficiency (e.g., the degree by which the data iscompressed through the encoding process) of chroma components, such thatcapturing greater detail does not need to result in an increase in thesize of the encoded data. As an example, use of a Linear Model (LM) mode(or “chroma prediction mode”), which predicts one or more chromacomponents from one or more reconstructed luma components, can improvethe coding efficiency of the chroma components. Using techniques such asthese, the chroma components cab have less reconstruction distortionthan the luma components.

In various examples, video coding processes and devices can adaptivelyselect chroma QP values. For example, different lookup tables can beused for different situations, where the lookup table provides arelationship between luma QP and chroma QP values. A different lookuptable can be selected, for example, based on the current slice typeand/or the current prediction mode, among other factors. In someexamples, a luminance value can be used, in addition to or instead ofthe slice type and/or prediction mode, to select a luma QP and chroma QPrelationship table. The human visual system can have differentsensitivity levels for color under different luminance conditions. Usingluminance as a factor in selecting chroma QP values can thus improvecoding efficiency and/or better capture color details that can be seenby the human eye.

As an example, the current prediction mode can be used to select a lumaQP and chroma QP relationship table. For example, when the predictionmode for a current slice is an intra-picture mode, Table 1 above can beused to select chroma QP values using luma QP values, and when thecurrent prediction mode is an inter-prediction mode (e.g., as may be thecase of P-slices and B-slices), the example values in Table 2 below canbe used. In this example, QP differences are reduced for slices beingpredicted with inter-prediction when the luma QP values are high, ascompared to the QP differences used for intra-predicted slices.

TABLE 2 Luma QP 0 1 2 3 4 5 6 7 8 Chroma QP 0 1 2 3 4 5 6 7 8 Luma QP 910 11 12 13 14 15 16 17 Chroma QP 9 10 11 12 13 14 15 16 17 Luma QP 1819 20 21 22 23 24 25 26 Chroma QP 18 19 20 21 22 23 24 25 26 Luma QP 2728 29 30 31 32 33 34 35 Chroma QP 27 28 29 29 30 31 32 33 33 Luma QP 3637 38 39 40 41 42 43 44 Chroma QP 34 35 36 36 37 37 38 39 40 Luma QP 4546 47 48 49 50 51 52 53 Chroma QP 41 42 43 44 45 46 47 48 49 Luma QP 5455 56 57 Chroma QP 50 51 52 53

In various examples, different luma QP and chroma QP relationship tablescan, alternatively or additionally, be used at the block level. Forexample, Table 1 can be used for intra-predicted blocks, and Table 2 canbe used for inter-predicted blocks. As another example, Table 1 can beused for intra-predicted blocks, and Table 2 can be used for blockspredicted with LM mode and/or inter-predicted blocks.

In some examples, different luma QP and chroma QP relationship tablescan, alternatively or additionally, be used for pictures coded indifferent temporal layers (e.g., pictures with different temporal layeridentifiers).

In various, different or additional lookup tables to Table 1 and Table 2can be defined, which can be selected from at each the block, slice,picture, or temporal layer.

In various examples, the luma QP and chroma QP relationship tables canbe predefined, such that encoders and decoders can each have copies ofthe tables. In these examples, the tables would not need to be signaled(e.g., encoded and/or transmitted) from an encoder to a decoder.Instead, an index can be signaled from the encoded to the decoder toindicate which table to apply, and at which level the table is to beapplied. For example, the encoder can indicate a lookup table to applyat the sequence level (e.g., in a Sequence Parameter Set (SPS)), at thepicture level (e.g., in a Picture Parameter Set (PPS)), at the slicelevel (e.g., in a Slice header), at the block level (e.g., in CodingTree Unit (CTU), Coding Unit (CU), Transform Unit (TU) or at any othersuitable block level), and/or at any other suitable level. In somecases, the index can be signaled in a supplemental enhancementinformation (SEI) message.

In some examples, one or more luma QP and chroma QP relationship tablescan sent from the encoder to the decoder. The encoder can transmit atable at any level, such as at the sequence level (e.g., in a SequenceParameter Set (SPS)), at the picture level (e.g., in a Picture ParameterSet (PPS), at slice level (e.g., in a Slice header), as a SupplementalEnhancement Information (SEI) message, and/or as a video usabilityinformation (VUI).

In various examples, an encoding device can be configured to adaptivelyuse multiple luma QP and chroma QP relationship tables. FIG. 4 includesa block diagram of a quantization unit 402 that can be included in anencoding device. As discussed further below, the encoding device caninclude the quantization unit 402 among other components that theencoding device uses to encode video data. In various examples, thequantization unit 402 receives transform coefficients 410 from atransform processing unit, and outputs quantized residual transformcoefficients 414. The quantized residual transform coefficients 414 canundergo entropy encoding before being added to an encoded bitstream.

In the example of FIG. 4, the quantization unit 402 includes multiple QPtables 420, which can include, for example, Table 1 and Table 2 asdiscussed above, and/or other tables. The QP tables 420 can be stored,for example, in a memory of the encoding device and/or can be loadedfrom a storage drive. The quantization unit 402 also includes a QPselection engine 422, which receives configuration parameters 412 thatcan be used to select QP values 424 to use in a quantization engine 416.In contrast, other quantization unit implementations may include onlyone QP table and a simpler QP selection engine that only needs toperform lookups within the one QP table.

In various examples, the configuration parameters 412 can be derivedfrom the current coding state of the encoding device. For example, theconfiguration parameters 412 can indicate, for a current coding unit, acurrent slice type, a current prediction mode, and/or a currentluminance value, among other parameters. In this and other examples, theQP selection engine 422 can use one or more of the configurationparameters 412 to select a particular QP table from among the availableQP tables 420. In various examples, the configuration parameters 412 analso include a current luma QP value, which the QP selection engine 422can use to look up a chroma QP value from the selected QP table.

Having determined a chroma QP value, the QP selection engine 422 canprovide the luma QP and chroma QP values 424 to a quantization engine416. The quantization engine 416 can use the QP values 424 to perform aquantization on the transform coefficients 410 to produce the quantizedresidual transform coefficients 414.

FIG. 5 includes a block diagram illustrating an example of an inversequantization unit 504 that can be included in an encoding device or adecoding device (either of which can be referred to as a coding device).An encoding device can include an inverse quantization unit 504 forgenerating reconstructed blocks, which can be used in predictionprocessing. A decoding device can include an inverse quantization unit504 to reconstruct the residual data that was determined in the encodingprocess. In both cases, the inverse quantization unit 504 performs theinverse of the quantization performed by the quantization unit of FIG.4, as a step in performing the reverse of the encoding process toreconstruct, as best as possible, the original video data.

The inverse quantization unit 504 receives as input quantizedcoefficients 514. In an encoding device, the quantized coefficients 514can be output by a quantization unit. In a decoding device, thequantized coefficients 514 an entropy decoding unit, which can performentropy decoding on an encoded video bitstream to product syntaxelements and the quantized coefficients 514. The inverse quantizationunit 504 can output transform coefficients 510, which a coding devicecan input into an inverse transform processing unit to produce residualdata.

In the example of FIG. 5, the inverse quantization unit 504 includesmultiple QP tables 520, which can include, for example, Table 1 andTable 2 as discussed above, and/or other tables. The QP tables 520 canbe stored, for example, in a memory of the coding device and/or can beloaded from a storage drive. The inverse quantization unit 504 alsoincludes a QP selection engine 522, which receives configurationparameters 512 that can be used to determine QP values 524 to use in aninverse quantization engine 518. In contrast, other inverse quantizationunit implementations may include only one QP table and a QP selectionengine that only need to perform lookups in the one QP table.

In various examples, the configuration parameters 512 can indicate acurrent decoding parameters. For example, the configuration parameters512 can indicate, for a current coding unit, a current slice type, acurrent prediction mode, and/or a current luminance value, among otherparameters. In this and other examples, the QP selection engine 522 canuse one or more of the configuration parameters 512 to select aparticular QP table from among the QP tables 520. Alternatively oradditionally, the configuration parameters 512 can include an index thatidentifies a particular QP table from the QP tables 520. The index canhave been determined by a quantization unit that determined the QP tableto use, and can have been included in the encoded video data.

In various examples, the configuration parameters 512 can also include aluma QP value. In these examples, the QP selection engine 522 candetermine a chroma QP value from the selected QP table. The QP selectionengine 522 can further provide the luma QP and the chroma QP to theinverse quantization engine 518. The inverse quantization engine 518 canuse the QP values 424 to perform an inverse quantization, and output thetransform coefficients 510.

FIG. 6 includes a flowchart illustrating an example of a process 600 forencoding video data. In various examples, the process 600 can beimplemented by an encoding device. An encoding device can include, forexample, a processor and a memory for storing video data. In someexamples, the encoding device can include a camera for capturing thevideo data. In some examples, the encoding device is a mobile device, oris included in a mobile device.

At step 602, the process 600 includes obtaining video data. The videodata can be obtained, for example, from a video capture device, such asa camera. Alternatively or additionally, in some examples, the videodata can be obtained from a storage location, such as a hard disk drive.Alternatively or additionally, in some examples, the video data can beobtained from a network, using, for example, network interface hardwareand networking software.

At step 604, the process 600 includes selecting, for a portion of thevideo data, a particular lookup table from a plurality of lookup tables,wherein each of the plurality of lookup tables defines relationshipsbetween luma quantization parameter values and chroma quantizationparameter values. The lookup tables can be configured, for example, sothat the luma quantization parameter value can be used to look up acorresponding chroma quantization parameter value. In some examples, thechroma quantization parameter value is at an offset from the lumaquantization parameter. In various examples, the same lookup tables canbe configured for a decoding device, so that the lookup tables do notneed to be included in the encoded video data.

In various examples, the encoding device can be pre-configured with aset of lookup tables, where each lookup table defines different chromaquantization parameter values for the possible luma quantizationparameter values. In some examples, the process 600 further includesdetermining a slice type for the portion of the video data. In theseexamples, the particular lookup table can be selected using the slicetype. The slice type can be, for example, I, P, or B, forintra-predicted slices, inter-predicted slices using one referencepicture, and inter-predicted slices using two reference pictures,respectively. In some examples, the process 600 further includesdetermining a prediction mode for the portion of the video data. Inthese examples, the particular lookup table can be selected using theprediction mode. The prediction mode can be an intra-prediction mode oran inter-prediction mode, for example. In some examples, the process 600further includes determining a luminance value for a pixel in theportion of the video data. In these examples, the particular lookuptable can be selected using the luminance value. The luminance valuecan, for example, be determined from a representative pixel in thecoding unit. Alternatively or additionally, as another example, theluminance value can be an average value for the pixels in the codingunit. Alternatively or additionally, the luminance value can be from aprevious coding unit or a reference coding unit. In various examples,other techniques can be used to determine the luminance value.

At step 606, the process 600 includes determining, for a coding unitfrom the portion of the video data, a luma quantization parameter value.The luma quantization parameter value can be determined, for example,from a previously-used luma quantization parameter value, the locationof the portion of the video data within a video frame, and/or anencoding quality level selected for the video data, among other factors.

At step 608, the process 600 includes determining, for the coding unit,a chroma quantization parameter value, wherein the chroma quantizationparameter value is determined by using the luma quantization parametervalue to look up the chroma quantization parameter value in theparticular lookup table.

At step 610, the process 600 includes performing quantization on thecoding unit using the luma quantization parameter value and the chromaquantization parameter value. Performing quantization can occur, forexample, after the encoding device has performed motion estimationand/or motion compensation to determine residual values for the codingunit. In these examples, quantization can be performed on the residualvalues. Performing quantization can include using the luma quantizationparameter value and the chroma quantization parameter value to reduceluma values and chroma values, respectively, to discrete values.

At step 612, the process 600 includes generating encoded video datausing values determined from performing quantization on the coding unit.For example, the values determined from performing quantization canundergo entropy encoding to produce syntax elements that are added tothe encoded video data. In various examples, the output of the process600 is an encoded bitstream, which can be stored, transmitted, and/ordecoded for display.

In some examples, the encoded video data includes an index thatidentifies the particular lookup table. For example, in generating theencoded video data, the encoding device can include the index in theencoded video data. The index can be included, for example, in an SPSNAL unit, a PPS NAL unit, in a slice header, and/or in a block-levelindicator, among other possible locations. Alternatively oradditionally, the index can be included in an SEI message and/or in aVUI message, among other examples.

In some examples, the process 600 further includes encoding theparticular table into the encoded video data. In these examples, theparticular table can be included in an SPS NAL unit, in a PPS NAL unit,in a slice header, in an SEI message, and/or in a VUI NAL unit, amongother possible locations.

FIG. 7 includes a flowchart illustrating an example of a process 700 fordecoding video data. In various examples, the process 600 can beimplemented by an encoding device or a decoding device, either of whichcan be referred to as a coding device. A coding device can include, forexample, a processor and a memory for storing encoded video data. Insome examples, the coding device includes a camera for capturing videodata and/or a display for displaying decoded video. In some examples,the coding device is a mobile device, or is included in a mobile device.

At step 702, the process 700 includes obtaining encoded video data. Theencoded video data can be obtained, for example, from a storagelocation, such as a memory or a hard disk. Alternatively oradditionally, in some examples, the encoded video data can be obtainedfrom a network.

At step 704, the process 700 selecting, for a portion of the encodedvideo data, a particular lookup table from a plurality of lookup tables,wherein each of the plurality of lookup tables defines a relationshipbetween luma quantization parameter values and chroma quantizationparameter values. The lookup tables can be configured, for example, sothat the luma quantization parameter value can be used to look up acorresponding chroma quantization parameter value. In some examples, thechroma quantization parameter value is at an offset from the lumaquantization parameter. In various examples, a decoding device can beconfigured with the same lookup tables that were used by an encodingdevice that encoded the video data, so that the lookup tables do notneed to be transmitted to the decoding device.

In various examples, a coding device can be pre-configured with a set oflookup tables, where each lookup table defines different chromaquantization parameter values for the possible luma quantizationparameter values. In some examples, the process 700 includes determininga slice type for the portion of the encoded video data. In theseexamples, the particular lookup table can be selected using the slicetype. The slice type can be, for example, one of an I, P, or B slice. Insome examples, the process 700 includes determining a prediction modefor the portion of the encoded video data. In these examples, theparticular lookup table can be selected using the prediction mode. Theprediction mode can be one of multiple different types ofintra-prediction modes and inter-prediction modes. In some examples, theprocess 700 includes determining a luminance value for a pixel in theportion of the encoded video data. In these examples, the particularlookup table can be selected using the luminance value. The luminancevalue can be a representative luminance value for the coding unit, canbe from a previous coding unit, can be from a reference coding unit,and/or can come from another source. In some examples, the process 700can include determining, from the encoded video data, an index, wherethe particular lookup table is selected using the index. The index canbe included, for example, in an SPS NAL unit, a PPS NAL unit, a sliceheader, in block-level information, in an SEI message, and/or in a VUImessage, among other locations.

In some examples, the process 700 can further include decoding theparticular lookup table from the encoded video data. In these examples,the particular lookup table was included in the encoded video data, forexample in an SPS NAL unit, a PPS NAL unit, a slice header, inblock-level information, in an SEI message, and/or in a VUI message,among other possible locations

At step 706, the process 700 includes determining, for a coding unitfrom the portion of the encoded video data, a luma quantizationparameter value. The luma quantization parameter value can be determinedfrom, for example, a previous luma quantization parameter value, alocation of the coding unit in a video frame, and/or an encoding valueselected for the encoded video data. For example, the luma quantizationparameter value can be included in a syntax element in the encoded videodata.

At step 708, the process 700 includes determining, for the coding unit,a chroma quantization parameter value, wherein the chroma quantizationparameter value is determined by using the luma quantization parametervalue to look up the chroma quantization parameter value in theparticular lookup table.

At step 710, the process 700 includes performing inverse quantization onthe coding unit using the luma quantization parameter value and thechroma quantization parameter value.

At step 712, the process 700 includes decoding the portion of theencoded video data using results from performing inverse quantization onthe coding unit. In some examples, performing inverse quantization in anencoding device can occur on quantized transform coefficients that areproduced be performing quantization on the transform coefficients. Inthese examples, performing inverse quantization can be part ofreconstructing the residual values determined by motion predictionand/or motion estimation. In a decoding device, various examples,inverse quantization can also be used to reconstruct residual values,which can then be used in the decoding device in motion estimation andmotion compensation to reconstruct the original video data. In variousexamples, the output of decoding the portion of the encoded video datais a portion of the video data from which the encoded video data wasgenerated.

The coding techniques discussed herein may be implemented in an examplevideo encoding and decoding system (e.g., system 100). In some examples,a system includes a source device that provides encoded video data to bedecoded at a later time by a destination device. In particular, thesource device provides the video data to destination device via acomputer-readable medium. The source device and the destination devicemay comprise any of a wide range of devices, including desktopcomputers, notebook (i.e., laptop) computers, tablet computers, set-topboxes, telephone handsets such as so-called “smart” phones, so-called“smart” pads, televisions, cameras, display devices, digital mediaplayers, video gaming consoles, video streaming device, or the like. Insome cases, the source device and the destination device may be equippedfor wireless communication.

The destination device may receive the encoded video data to be decodedvia the computer-readable medium. The computer-readable medium maycomprise any type of medium or device capable of moving the encodedvideo data from source device to destination device. In one example,computer-readable medium may comprise a communication medium to enablesource device to transmit encoded video data directly to destinationdevice in real-time. The encoded video data may be modulated accordingto a communication standard, such as a wireless communication protocol,and transmitted to destination device. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device to destination device.

In some examples, encoded data may be output from output interface to astorage device. Similarly, encoded data may be accessed from the storagedevice by input interface. The storage device may include any of avariety of distributed or locally accessed data storage media such as ahard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device. Destinationdevice may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In one example the source device includes a video source, a videoencoder, and a output interface. The destination device may include aninput interface, a video decoder, and a display device. The videoencoder of source device may be configured to apply the techniquesdisclosed herein. In other examples, a source device and a destinationdevice may include other components or arrangements. For example, thesource device may receive video data from an external video source, suchas an external camera. Likewise, the destination device may interfacewith an external display device, rather than including an integrateddisplay device.

The example system above is merely one example. Techniques forprocessing video data in parallel may be performed by any digital videoencoding and/or decoding device. Although generally the techniques ofthis disclosure are performed by a video encoding device, the techniquesmay also be performed by a video encoder/decoder, typically referred toas a “CODEC.” Moreover, the techniques of this disclosure may also beperformed by a video preprocessor. Source device and destination deviceare merely examples of such coding devices in which source devicegenerates coded video data for transmission to destination device. Insome examples, the source and destination devices may operate in asubstantially symmetrical manner such that each of the devices includevideo encoding and decoding components. Hence, example systems maysupport one-way or two-way video transmission between video devices,e.g., for video streaming, video playback, video broadcasting, or videotelephony.

The video source may include a video capture device, such as a videocamera, a video archive containing previously captured video, and/or avideo feed interface to receive video from a video content provider. Asa further alternative, the video source may generate computergraphics-based data as the source video, or a combination of live video,archived video, and computer generated video. In some cases, if videosource is a video camera, source device and destination device may formso-called camera phones or video phones. As mentioned above, however,the techniques described in this disclosure may be applicable to videocoding in general, and may be applied to wireless and/or wiredapplications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by the video encoder. Theencoded video information may then be output by output interface ontothe computer-readable medium.

As noted the computer-readable medium may include transient media, suchas a wireless broadcast or wired network transmission, or storage media(that is, non-transitory storage media), such as a hard disk, flashdrive, compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from the source device and provide theencoded video data to the destination device, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from the source device and produce a disc containing the encodedvideo data. Therefore, the computer-readable medium may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

The input interface of the destination device receives information fromthe computer-readable medium. The information of the computer-readablemedium may include syntax information defined by the video encoder,which is also used by the video decoder, that includes syntax elementsthat describe characteristics and/or processing of blocks and othercoded units, e.g., group of pictures (GOP). A display device displaysthe decoded video data to a user, and may comprise any of a variety ofdisplay devices such as a cathode ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device. Various embodiments of theapplication have been described.

Specific details of the encoding device 104 and the decoding device 112are shown in FIG. 8 and FIG. 9, respectively. FIG. 8 is a block diagramillustrating an example encoding device 104 that may implement one ormore of the techniques described in this disclosure. Encoding device 104may, for example, generate the syntax structures described herein (e.g.,the syntax structures of a VPS, SPS, PPS, or other syntax elements).Encoding device 104 may perform intra-prediction and inter-predictioncoding of video blocks within video slices. As previously described,intra-coding relies, at least in part, on spatial prediction to reduceor remove spatial redundancy within a given video frame or picture.Inter-coding relies, at least in part, on temporal prediction to reduceor remove temporal redundancy within adjacent or surrounding frames of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased compression modes. Inter-modes, such as uni-directional prediction(P mode) or bi-prediction (B mode), may refer to any of severaltemporal-based compression modes.

The encoding device 104 includes a partitioning unit 35, predictionprocessing unit 41, filter unit 63, picture memory 64, summer 50,transform processing unit 52, quantization unit 54, and entropy encodingunit 56. Prediction processing unit 41 includes motion estimation unit42, motion compensation unit 44, and intra-prediction processing unit46. For video block reconstruction, encoding device 104 also includesinverse quantization unit 58, inverse transform processing unit 60, andsummer 62. Filter unit 63 is intended to represent one or more loopfilters such as a deblocking filter, an adaptive loop filter (ALF), anda sample adaptive offset (SAO) filter. Although filter unit 63 is shownin FIG. 8 as being an in loop filter, in other configurations, filterunit 63 may be implemented as a post loop filter. A post processingdevice 57 may perform additional processing on encoded video datagenerated by the encoding device 104. The techniques of this disclosuremay in some instances be implemented by the encoding device 104. Inother instances, however, one or more of the techniques of thisdisclosure may be implemented by post processing device 57.

As shown in FIG. 9, the encoding device 104 receives video data, andpartitioning unit 35 partitions the data into video blocks. Thepartitioning may also include partitioning into slices, slice segments,tiles, or other larger units, as wells as video block partitioning,e.g., according to a quadtree structure of LCUs and CUs. The encodingdevice 104 generally illustrates the components that encode video blockswithin a video slice to be encoded. The slice may be divided intomultiple video blocks (and possibly into sets of video blocks referredto as tiles). Prediction processing unit 41 may select one of aplurality of possible coding modes, such as one of a plurality ofintra-prediction coding modes or one of a plurality of inter-predictioncoding modes, for the current video block based on error results (e.g.,coding rate and the level of distortion, or the like). Predictionprocessing unit 41 may provide the resulting intra- or inter-coded blockto summer 50 to generate residual block data and to summer 62 toreconstruct the encoded block for use as a reference picture.

Intra-prediction processing unit 46 within prediction processing unit 41may perform intra-prediction coding of the current video block relativeto one or more neighboring blocks in the same frame or slice as thecurrent block to be coded to provide spatial compression. Motionestimation unit 42 and motion compensation unit 44 within predictionprocessing unit 41 perform inter-predictive coding of the current videoblock relative to one or more predictive blocks in one or more referencepictures to provide temporal compression.

Motion estimation unit 42 may be configured to determine theinter-prediction mode for a video slice according to a predeterminedpattern for a video sequence. The predetermined pattern may designatevideo slices in the sequence as P slices, B slices, or GPB slices.Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aprediction unit (PU) of a video block within a current video frame orpicture relative to a predictive block within a reference picture.

A predictive block is a block that is found to closely match the PU ofthe video block to be coded in terms of pixel difference, which may bedetermined by sum of absolute difference (SAD), sum of square difference(SSD), or other difference metrics. In some examples, the encodingdevice 104 may calculate values for sub-integer pixel positions ofreference pictures stored in picture memory 64. For example, theencoding device 104 may interpolate values of one-quarter pixelpositions, one-eighth pixel positions, or other fractional pixelpositions of the reference picture. Therefore, motion estimation unit 42may perform a motion search relative to the full pixel positions andfractional pixel positions and output a motion vector with fractionalpixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in picture memory 64. Motion estimationunit 42 sends the calculated motion vector to entropy encoding unit 56and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Upon receiving the motion vectorfor the PU of the current video block, motion compensation unit 44 maylocate the predictive block to which the motion vector points in areference picture list. The encoding device 104 forms a residual videoblock by subtracting pixel values of the predictive block from the pixelvalues of the current video block being coded, forming pixel differencevalues. The pixel difference values form residual data for the block,and may include both luma and chroma difference components. Summer 50represents the component or components that perform this subtractionoperation. Motion compensation unit 44 may also generate syntax elementsassociated with the video blocks and the video slice for use by thedecoding device 112 in decoding the video blocks of the video slice.

Intra-prediction processing unit 46 may intra-predict a current block,as an alternative to the inter-prediction performed by motion estimationunit 42 and motion compensation unit 44, as described above. Inparticular, intra-prediction processing unit 46 may determine anintra-prediction mode to use to encode a current block. In someexamples, intra-prediction processing unit 46 may encode a current blockusing various intra-prediction modes, e.g., during separate encodingpasses, and intra-prediction processing 46 may select an appropriateintra-prediction mode to use from the tested modes. For example,intra-prediction processing unit 46 may calculate rate-distortion valuesusing a rate-distortion analysis for the various tested intra-predictionmodes, and may select the intra-prediction mode having the bestrate-distortion characteristics among the tested modes. Rate-distortionanalysis generally determines an amount of distortion (or error) betweenan encoded block and an original, unencoded block that was encoded toproduce the encoded block, as well as a bit rate (that is, a number ofbits) used to produce the encoded block. Intra-prediction processingunit 46 may calculate ratios from the distortions and rates for thevarious encoded blocks to determine which intra-prediction mode exhibitsthe best rate-distortion value for the block.

In any case, after selecting an intra-prediction mode for a block,intra-prediction processing unit 46 may provide information indicativeof the selected intra-prediction mode for the block to entropy encodingunit 56. Entropy encoding unit 56 may encode the information indicatingthe selected intra-prediction mode. The encoding device 104 may includein the transmitted bitstream configuration data definitions of encodingcontexts for various blocks as well as indications of a most probableintra-prediction mode, an intra-prediction mode index table, and amodified intra-prediction mode index table to use for each of thecontexts. The bitstream configuration data may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables).

After prediction processing unit 41 generates the predictive block forthe current video block via either inter-prediction or intra-prediction,the encoding device 104 forms a residual video block by subtracting thepredictive block from the current video block. The residual video datain the residual block may be included in one or more TUs and applied totransform processing unit 52. Transform processing unit 52 transformsthe residual video data into residual transform coefficients using atransform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform. Transform processing unit 52 may convert the residualvideo data from a pixel domain to a transform domain, such as afrequency domain.

Transform processing unit 52 may send the resulting transformcoefficients to quantization unit 54. Quantization unit 54 quantizes thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, quantization unit 54 may thenperform a scan of the matrix including the quantized transformcoefficients. Alternatively, entropy encoding unit 56 may perform thescan.

Following quantization, entropy encoding unit 56 entropy encodes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy encoding technique. Followingthe entropy encoding by entropy encoding unit 56, the encoded bitstreammay be transmitted to the decoding device 112, or archived for latertransmission or retrieval by the decoding device 112. Entropy encodingunit 56 may also entropy encode the motion vectors and the other syntaxelements for the current video slice being coded.

Inverse quantization unit 58 and inverse transform processing unit 60apply inverse quantization and inverse transformation, respectively, toreconstruct the residual block in the pixel domain for later use as areference block of a reference picture. Motion compensation unit 44 maycalculate a reference block by adding the residual block to a predictiveblock of one of the reference pictures within a reference picture list.Motion compensation unit 44 may also apply one or more interpolationfilters to the reconstructed residual block to calculate sub-integerpixel values for use in motion estimation. Summer 62 adds thereconstructed residual block to the motion compensated prediction blockproduced by motion compensation unit 44 to produce a reference block forstorage in picture memory 64. The reference block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-predict a block in a subsequent video frame or picture.

In this manner, the encoding device 104 of FIG. 8 represents an exampleof a video encoder configured to generate syntax for a encoded videobitstream. The encoding device 104 may, for example, generate VPS, SPS,and PPS parameter sets as described above. The encoding device 104 mayperform any of the techniques described herein. Some of the techniquesof this disclosure may be generally described with respect to theencoding device 104 or the decoding device 112, but as mentioned above,some of the techniques of this disclosure may also be implemented bypost processing device 57.

FIG. 9 is a block diagram illustrating an example decoding device 112.The decoding device 112 includes an entropy decoding unit 80, predictionprocessing unit 81, inverse quantization unit 86, inverse transformprocessing unit 88, summer 90, filter unit 91, and picture memory 92.Prediction processing unit 81 includes motion compensation unit 82 andintra prediction processing unit 84. The decoding device 112 may, insome examples, perform a decoding pass generally reciprocal to theencoding pass described with respect to the encoding device 104 fromFIG. 8.

During the decoding process, the decoding device 112 receives an encodedvideo bitstream that represents video blocks of an encoded video sliceand associated syntax elements sent by the encoding device 104. In someembodiments, the decoding device 112 may receive the encoded videobitstream from the encoding device 104. In some embodiments, thedecoding device 112 may receive the encoded video bitstream from anetwork entity 79, such as a server, a media-aware network element(MANE), a video editor/splicer, or other such device configured toimplement one or more of the techniques described above. Network entity79 may or may not include the encoding device 104. Some of thetechniques described in this disclosure may be implemented by networkentity 79 prior to network entity 79 transmitting the encoded videobitstream to the decoding device 112. In some video decoding systems,network entity 79 and the decoding device 112 may be parts of separatedevices, while in other instances, the functionality described withrespect to network entity 79 may be performed by the same device thatcomprises the decoding device 112.

The entropy decoding unit 80 of the decoding device 112 entropy decodesthe bitstream to generate quantized coefficients, motion vectors, andother syntax elements. Entropy decoding unit 80 forwards the motionvectors and other syntax elements to prediction processing unit 81. Thedecoding device 112 may receive the syntax elements at the video slicelevel and/or the video block level. Entropy decoding unit 80 may processand parse both fixed-length syntax elements and variable-length syntaxelements in or more parameter sets, such as a VPS, SPS, and PPS.

When the video slice is coded as an intra-coded (I) slice, intraprediction processing unit 84 of prediction processing unit 81 maygenerate prediction data for a video block of the current video slicebased on a signaled intra-prediction mode and data from previouslydecoded blocks of the current frame or picture. When the video frame iscoded as an inter-coded (i.e., B, P or GPB) slice, motion compensationunit 82 of prediction processing unit 81 produces predictive blocks fora video block of the current video slice based on the motion vectors andother syntax elements received from entropy decoding unit 80. Thepredictive blocks may be produced from one of the reference pictureswithin a reference picture list. The decoding device 112 may constructthe reference frame lists, List 0 and List 1, using default constructiontechniques based on reference pictures stored in picture memory 92.

Motion compensation unit 82 determines prediction information for avideo block of the current video slice by parsing the motion vectors andother syntax elements, and uses the prediction information to producethe predictive blocks for the current video block being decoded. Forexample, motion compensation unit 82 may use one or more syntax elementsin a parameter set to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more reference picture lists for theslice, motion vectors for each inter-encoded video block of the slice,inter-prediction status for each inter-coded video block of the slice,and other information to decode the video blocks in the current videoslice.

Motion compensation unit 82 may also perform interpolation based oninterpolation filters. Motion compensation unit 82 may use interpolationfilters as used by the encoding device 104 during encoding of the videoblocks to calculate interpolated values for sub-integer pixels ofreference blocks. In this case, motion compensation unit 82 maydetermine the interpolation filters used by the encoding device 104 fromthe received syntax elements, and may use the interpolation filters toproduce predictive blocks.

Inverse quantization unit 86 inverse quantizes, or de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 80. The inverse quantization process mayinclude use of a quantization parameter calculated by the encodingdevice 104 for each video block in the video slice to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied. Inverse transform processing unit 88 applies aninverse transform (e.g., an inverse DCT or other suitable inversetransform), an inverse integer transform, or a conceptually similarinverse transform process, to the transform coefficients in order toproduce residual blocks in the pixel domain.

After motion compensation unit 82 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, the decoding device 112 forms a decoded video block by summingthe residual blocks from inverse transform processing unit 88 with thecorresponding predictive blocks generated by motion compensation unit82. Summer 90 represents the component or components that perform thissummation operation. If desired, loop filters (either in the coding loopor after the coding loop) may also be used to smooth pixel transitions,or to otherwise improve the video quality. Filter unit 91 is intended torepresent one or more loop filters such as a deblocking filter, anadaptive loop filter (ALF), and a sample adaptive offset (SAO) filter.Although filter unit 91 is shown in FIG. 9 as being an in loop filter,in other configurations, filter unit 91 may be implemented as a postloop filter. The decoded video blocks in a given frame or picture arethen stored in picture memory 92, which stores reference pictures usedfor subsequent motion compensation. Picture memory 92 also storesdecoded video for later presentation on a display device, such as videodestination device 122 shown in FIG. 1.

In the foregoing description, aspects of the application are describedwith reference to specific embodiments thereof, but those skilled in theart will recognize that the application is not limited thereto. Thus,while illustrative embodiments of the application have been described indetail herein, it is to be understood that the inventive concepts may beotherwise variously embodied and employed, and that the appended claimsare intended to be construed to include such variations, except aslimited by the prior art. Various features and aspects of theabove-described application may be used individually or jointly.Further, embodiments can be utilized in any number of environments andapplications beyond those described herein without departing from thebroader spirit and scope of the specification. The specification anddrawings are, accordingly, to be regarded as illustrative rather thanrestrictive. For the purposes of illustration, methods were described ina particular order. It should be appreciated that in alternateembodiments, the methods may be performed in a different order than thatdescribed.

Where components are described as being “configured to” perform certainoperations, such configuration can be accomplished, for example, bydesigning electronic circuits or other hardware to perform theoperation, by programming programmable electronic circuits (e.g.,microprocessors, or other suitable electronic circuits) to perform theoperation, or any combination thereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software,firmware, or combinations thereof. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present application.

The techniques described herein may also be implemented in electronichardware, computer software, firmware, or any combination thereof. Suchtechniques may be implemented in any of a variety of devices such asgeneral purposes computers, wireless communication device handsets, orintegrated circuit devices having multiple uses including application inwireless communication device handsets and other devices. Any featuresdescribed as modules or components may be implemented together in anintegrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a computer-readable data storage mediumcomprising program code including instructions that, when executed,performs one or more of the methods described above. Thecomputer-readable data storage medium may form part of a computerprogram product, which may include packaging materials. Thecomputer-readable medium may comprise memory or data storage media, suchas random access memory (RAM) such as synchronous dynamic random accessmemory (SDRAM), read-only memory (ROM), non-volatile random accessmemory (NVRAM), electrically erasable programmable read-only memory(EEPROM), FLASH memory, magnetic or optical data storage media, and thelike. The techniques additionally, or alternatively, may be realized atleast in part by a computer-readable communication medium that carriesor communicates program code in the form of instructions or datastructures and that can be accessed, read, and/or executed by acomputer, such as propagated signals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor,” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured for encodingand decoding, or incorporated in a combined video encoder-decoder(CODEC).

What is claimed is:
 1. A method of encoding video data, comprising:obtaining, at an encoding device, video data; selecting, for a portionof the video data, a particular lookup table from a plurality of lookuptables, wherein each of the plurality of lookup tables definesrelationships between luma quantization parameter values and chromaquantization parameter values; determining, for a coding unit from theportion of the video data, a luma quantization parameter value;determining, for the coding unit, a chroma quantization parameter value,wherein the chroma quantization parameter value is determined by usingthe luma quantization parameter value to look up the chroma quantizationparameter value in the particular lookup table; performing quantizationon the coding unit using the luma quantization parameter value and thechroma quantization parameter value; and generating encoded video datausing values determined from performing quantization on the coding unit.2. The method of claim 1, further comprising: determining a slice typefor the portion of the video data, wherein the particular lookup tableis selected using the slice type.
 3. The method of claim 1, furthercomprising: determining a prediction mode for the portion of the videodata, wherein the particular lookup table is selected using theprediction mode.
 4. The method of claim 1, further comprising:determining a luminance value for a pixel in the portion of the videodata, wherein the particular lookup table is selected using theluminance value.
 5. The method of claim 1, wherein the encoded videodata includes an index that identifies the particular lookup table. 6.The method of claim 1, further comprising: encoding the particular tableinto the encoded video data.
 7. An encoding device, comprising: a memoryconfigured to store video data; and a processor configured to: select,for a portion of the video data, a particular lookup table from aplurality of lookup tables, wherein each of the plurality of lookuptables defines relationships between luma quantization parameter valuesand chroma quantization parameter values; determine, for a coding unitfrom the portion of the video data, a luma quantization parameter value;determine, for the coding unit, a chroma quantization parameter value,wherein the chroma quantization parameter value is determined by usingthe luma quantization parameter value to look up the chroma quantizationparameter value in the particular lookup table; perform quantization onthe coding unit using the luma quantization parameter value and thechroma quantization parameter value; and generate encoded video datausing values determined from performing quantization on the coding unit.8. The encoding device of claim 7, wherein the processor is furtherconfigured to: determine a slice type for the portion of the video data,wherein the particular lookup table is selected using the slice type. 9.The encoding device of claim 7, wherein the processor is furtherconfigured to: determine a prediction mode for the portion of the videodata, wherein the particular lookup table is selected using theprediction mode.
 10. The encoding device of claim 7, wherein theprocessor is further configured to: determine a luminance value for apixel in the portion of the video data, wherein the particular lookuptable is selected using the luminance value.
 11. The encoding device ofclaim 7, wherein the encoded video data includes an index thatidentifies the particular lookup table.
 12. The encoding device of claim7, wherein the processor is further configured to: encode the particulartable, wherein the encoded video data includes the encoded particulartable.
 13. The encoding device of claim 7, further comprising: a camerafor capturing video data.
 14. A non-transitory computer-readable mediumhaving stored thereon instructions that, when executed by one or moreprocessors of an encoding device, cause the one or more processors toperform operations including: obtaining video data; selecting, for aportion of the video data, a particular lookup table from a plurality oflookup tables, wherein each of the plurality of lookup tables definesrelationships between luma quantization parameter values and chromaquantization parameter values; determining, for a coding unit from theportion of the video data, a luma quantization parameter value;determining, for the coding unit, a chroma quantization parameter value,wherein the chroma quantization parameter value is determined by usingthe luma quantization parameter value to look up the chroma quantizationparameter value in the particular lookup table; performing quantizationon the coding unit using the luma quantization parameter value and thechroma quantization parameter value; and generating encoded video datausing values determined from performing quantization on the coding unit.15. An apparatus, comprising: means for obtaining video data; means forselecting, for a portion of the video data, a particular lookup tablefrom a plurality of lookup tables, wherein each of the plurality oflookup tables defines relationships between luma quantization parametervalues and chroma quantization parameter values; means for determining,for a coding unit from the portion of the video data, a lumaquantization parameter value; means for determining, for the codingunit, a chroma quantization parameter value, wherein the chromaquantization parameter value is determined by using the lumaquantization parameter value to look up the chroma quantizationparameter value in the particular lookup table; means for performingquantization on the coding unit using the luma quantization parametervalue and the chroma quantization parameter value; and means forgenerating encoded video data using values determined from performingquantization on the coding unit.
 16. A method of decoding video data,comprising: obtaining, at a coding device, encoded video data;selecting, for a portion of the encoded video data, a particular lookuptable from a plurality of lookup tables, wherein each of the pluralityof lookup tables defines a relationship between luma quantizationparameter values and chroma quantization parameter values; determining,for a coding unit from the portion of the encoded video data, a lumaquantization parameter value; determining, for the coding unit, a chromaquantization parameter value, wherein the chroma quantization parametervalue is determined by using the luma quantization parameter value tolook up the chroma quantization parameter value in the particular lookuptable; performing inverse quantization on the coding unit using the lumaquantization parameter value and the chroma quantization parametervalue; and decoding the portion of the encoded video data using resultsfrom performing inverse quantization on the coding unit.
 17. The methodof claim 16, further comprising: determining a slice type for theportion of the encoded video data, wherein the particular lookup tableis selected using the slice type.
 18. The method of claim 16, furthercomprising: determining a prediction mode for the portion of the encodedvideo data, wherein the particular lookup table is selected using theprediction mode.
 19. The method of claim 16, further comprising:determining a luminance value for a pixel in the portion of the encodedvideo data, wherein the particular lookup table is selected using theluminance value.
 20. The method of claim 16, further comprising:determining, from the encoded video data, an index, wherein theparticular lookup table is selected using the index.
 21. The method ofclaim 16, further comprising: decoding the particular lookup table fromthe encoded video data.
 22. A coding device, comprising: a memoryconfigured to store encoded video data; and a processor configured to:select, for a portion of the encoded video data, a particular lookuptable from a plurality of lookup tables, wherein each of the pluralityof lookup tables defines a relationship between luma quantizationparameter values and chroma quantization parameter values; determine,for a coding unit from the portion of the encoded video data, a lumaquantization parameter value; determine, for the coding unit, a chromaquantization parameter value, wherein the chroma quantization parametervalue is determined by using the luma quantization parameter value tolook up the chroma quantization parameter value in the particular lookuptable; perform inverse quantization on the coding unit using the lumaquantization parameter value and the chroma quantization parametervalue; and decode the portion of the encoded video data using resultsfrom performing inverse quantization on the coding unit.
 23. The codingdevice of claim 22, wherein the processor is further configured to:determine a slice type for the portion of the encoded video data,wherein the particular lookup table is selected using the slice type.24. The coding device of claim 22, wherein the processor is furtherconfigured to: determine a prediction mode for the portion of theencoded video data, wherein the particular lookup table is selectedusing the prediction mode.
 25. The coding device of claim 22, whereinthe processor is further configured to: determine a luminance value fora pixel in the portion of the encoded video data, wherein the particularlookup table is selected using the luminance value.
 26. The codingdevice of claim 22, wherein the processor is further configured to:determine, from the encoded video data, an index, wherein the particularlookup table is selected using the index.
 27. The coding device of claim22, wherein the processor is further configured to: decode theparticular lookup table from the encoded video data.
 28. The codingdevice of claim 22, further comprising: a camera for capturing videodata.
 29. The coding device of claim 22, further comprising: a displayfor displaying decoded video data.
 30. The coding device of claim 22,wherein the coding device comprises a mobile device with a camera forcapturing video data and a display for displaying the video data.
 31. Anon-transitory computer-readable medium having stored thereoninstructions that, when executed by one or more processors of a codingdevice, cause the one or more processors to perform operationsincluding: obtaining encoded video data; selecting, for a portion of theencoded video data, a particular lookup table from a plurality of lookuptables, wherein each of the plurality of lookup tables defines arelationship between luma quantization parameter values and chromaquantization parameter values; determining, for a coding unit from theportion of the encoded video data, a luma quantization parameter value;determining, for the coding unit, a chroma quantization parameter value,wherein the chroma quantization parameter value is determined by usingthe luma quantization parameter value to look up the chroma quantizationparameter value in the particular lookup table; performing inversequantization on the coding unit using the luma quantization parametervalue and the chroma quantization parameter value; and decoding theportion of the encoded video data using results from performing inversequantization on the coding unit.
 32. An apparatus, comprising: means forobtaining encoded video data; means for selecting, for a portion of theencoded video data, a particular lookup table from a plurality of lookuptables, wherein each of the plurality of lookup tables defines arelationship between luma quantization parameter values and chromaquantization parameter values; means for determining, for a coding unitfrom the portion of the encoded video data, a luma quantizationparameter value; means for determining, for the coding unit, a chromaquantization parameter value, wherein the chroma quantization parametervalue is determined by using the luma quantization parameter value tolook up the chroma quantization parameter value in the particular lookuptable; means for performing inverse quantization on the coding unitusing the luma quantization parameter value and the chroma quantizationparameter value; and means for decoding the portion of the encoded videodata using results from performing inverse quantization on the codingunit.